U.S. patent application number 10/012774 was filed with the patent office on 2002-05-02 for non-invasive in vivo pressure measurement.
Invention is credited to Madsen, Joseph R., Taylor, George A..
Application Number | 20020052550 10/012774 |
Document ID | / |
Family ID | 22260783 |
Filed Date | 2002-05-02 |
United States Patent
Application |
20020052550 |
Kind Code |
A1 |
Madsen, Joseph R. ; et
al. |
May 2, 2002 |
Non-invasive in vivo pressure measurement
Abstract
Apparatus and methods are disclosed for non-invasive measurement
of blood velocity in otherwise inaccessible body regions, and for
correlating such measurements with externally applied pressure to
detect and/or assess diseases or physiological abnormalities. The
blood velocity measurements can be based on the Doppler shift that
occurs when an ultrasonic wave is scattered by moving particles
within the blood. Since blood vessels have elastic walls, the
geometry of the walls, and therefore the flow dynamics, will change
in response to elevated in vivo pressure. The change in resistance
to blood flow resulting from these pressure induced changes to the
blood vessel wall geometry can provide a measure of intracranial
pressure, ophthalmic pressure or various other body conditions that
affect blood perfusion. Since the blood vessel wall geometry
changes rapidly in response to such changes in pressure, the
invention can be used to detect hydrocephalus, retinopathy,
papilledema and other physiological abnormalities manifested by
pressure changes.
Inventors: |
Madsen, Joseph R.; (Newton,
MA) ; Taylor, George A.; (Wellesley, MA) |
Correspondence
Address: |
NUTTER MCCLENNEN & FISH LLP
ONE INTERNATIONAL PLACE
BOSTON
MA
02110
US
|
Family ID: |
22260783 |
Appl. No.: |
10/012774 |
Filed: |
October 30, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10012774 |
Oct 30, 2001 |
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09613648 |
Jul 11, 2000 |
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09613648 |
Jul 11, 2000 |
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09097067 |
Jun 12, 1998 |
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Current U.S.
Class: |
600/438 |
Current CPC
Class: |
A61B 8/04 20130101; A61B
5/0053 20130101; A61B 8/0808 20130101; A61B 8/06 20130101 |
Class at
Publication: |
600/438 |
International
Class: |
A61B 008/00 |
Claims
It is also to be understood that the following claims are intended
to cover all generic and specific features of the invention
described herein. When describing the invention, what is claimed as
new and secured by Letters Patent is:
1. An apparatus for ultrasonically evaluating an in vivo pressure,
the apparatus comprising: an ultrasonic transducer for transmitting
a first ultrasonic wave to an in vivo target region and detecting a
second ultrasonic wave reflected from the in vivo target region; a
pressure applicator acoustically coupled to the ultrasonic
transducer for applying an external pressure to the target region,
the pressure applicator being filled with an acoustically
transmissive medium for propagation of the first and second
ultrasonic waves between the transducer and the target region; a
pressure sensor coupled to the pressure applicator for measuring
the external pressure applied by the pressure applicator; and a
data processor in communication with the pressure sensor and the
ultrasonic transducer for evaluating an in vivo pressure based on
the external pressure and the first and second ultrasonic
waves.
2. The apparatus according to claim 1 wherein the pressure
applicator comprises a bladder filled with an acoustically
transmissive medium.
3. The apparatus of claim 1 wherein the acoustically transmissive
medium comprises a liquid.
4. The apparatus of claim 3 wherein the liquid is water.
5. The apparatus of claim 1 wherein the ultrasonic transducer is
adapted to detect a second ultrasonic wave which is a Doppler
shifted transformation of the first ultrasonic wave.
6. The apparatus of claim 1 wherein the pressure applicator is
adapted for placement against a fontanelle on the neonatal
cranium.
7. A method for ultrasonically evaluating an in vivo pressure, the
method comprising the steps of: transmitting a first ultrasonic
wave into the target region; applying a pressure applicator filled
with an acoustically transmissive medium to the target region,
thereby developing an external pressure in the target region;
detecting a second ultrasonic wave, the second ultrasonic wave
generated by an interaction between the first ultrasonic wave and
the target region; measuring the applied external pressure, thereby
generating an external pressure measurement; calculating the in
vivo pressure in the target region based on the first and second
ultrasonic waves and on the external pressure measurement.
8. The method of claim 7 wherein the step of applying an external
pressure to the target region comprises the step of placing a
bladder against the target region, the bladder being filled with an
acoustically transmissive medium.
9. The method of claim 8 wherein the step of measuring the applied
external pressure comprises the step of providing a transducer
coupled to the bladder.
10. The method according to claim 7 wherein the acoustically
transmissive medium is a liquid.
11. The method according to claim 10 wherein the liquid is
water.
12. The method according to claim 7 wherein the step of detecting a
second ultrasonic wave comprises the step of detecting a Doppler
shifted transformation of the first ultrasonic wave.
13. The method according to claim 7 further comprising the step of
selecting the target region to be a neonatal cranium and the step
of measuring the applied external pressure includes the step of
placing the pressure applicator against a fontanelle on the
cranium.
14. A pressure applicator for coupling to an ultrasonic probe, the
pressure applicator comprising: a bladder containing an
acoustically transmissive medium, the bladder having a contact
surface for exerting an applied pressure against a target region,
and a side wall; a housing enclosing at least a portion of the
bladder to provide support for the bladder; and for coupling the
bladder to an ultrasonic probe, thereby permitting ultrasonic waves
to propagate through the bladder between the ultrasonic probe and
the target region.
15. The applicator of claim 14 wherein the applicator further
comprises a pressure transducer coupled to the bladder to provide a
measurement of pressure applied by the contact surface.
16. The applicator of claim 14 wherein the applicator further
comprises a pressure regulator for regulating the pressure applied
by the bladder.
Description
BACKGROUND OF THE INVENTION
[0001] The technical field of this invention is medical sonography
and, in particular, methods and devices for employing ultrasonic
measurements of blood flow to detect and assess diseases or
physiological abnormalities.
[0002] Inside the brain is a ventricular system which contains and
conducts cerebrospinal fluid. This cerebrospinal fluid flows
through several ventricles within the brain before being absorbed
back into the blood. When drainage is blocked, the buildup of fluid
results in a pressure which swells the ventricles and increases the
pressure throughout the brain. This causes a condition referred to
as "hydrocephalus."
[0003] Although the intracranial pressure increase associated with
hydrocephalus can be relieved surgically by providing a shunt from
the ventricle to the peritoneum, this too can frequently result in
complications. Accordingly, it is desirable to provide a method and
apparatus for reliably measuring the intracranial pressure.
[0004] Intracranial pressure can be measured directly by surgically
inserting a pressure transducer inside the cranium. However, the
inconvenience of surgery and the necessity of penetrating the skull
make this method undesirable.
[0005] Indirect evidence of intracranial pressure can be obtained
by observing the effect of elevated pressure on the structures
inside the cranium. For example, one can ultrasonically measure the
size of the ventricle and determine whether it is unusually large
or whether it has increased in size.
[0006] However, a hemorrhage, either inside the ventricle or in
adjacent parenchymal tissue, can obscure the ventricle and make
inferences about pressure from observation of its size difficult.
Since hydrocephalus is a frequent complication of intracranial
hemorrhage in premature infants, this difficulty is frequently
encountered in practice.
[0007] An additional disadvantage of the above method is that
detectable enlargement of the ventricle requires that the
hydrocephalus be chronic. Thus, by the time the elevated
intracranial pressure is detected, some damage may have already
occurred to the intracranial structures.
[0008] The difficulty in obtaining the intracranial pressure, as
described above, is a manifestation of the more general difficulty
of measuring pressure at inaccessible locations within the human
body. The process of measuring pressure in, for example, a blood
vessel, involves the application of a mechanical pressure to the
vessel itself. Typically, an inflatable cuff is placed around an
arm and inflated until it cuts off the blood flow. The cuff
pressure required to stop the blood flow provides a measure of the
pressure driving that flow.
[0009] The foregoing method of applying a mechanical pressure to a
blood vessel is not well suited for the measurement of pressure in
specific blood vessels. For example, in a diabetic patient
afflicted with papilledema, it is often desirable to measure the
blood pressure in the capillaries leading to the eye. The use of
the conventional inflatable cuff to measure blood pressure within
the capillaries leading to the retina is made difficult by the lack
of a suitable site at which to apply the inflatable cuff.
[0010] In some cases, even when a suitable pressure application
site is available, the process of inflating the cuff until it cuts
off blood flow may be highly intrusive. For example, measurement of
local blood pressure using a cuff in connection with the treatment
of impotence is hardly a practical option.
[0011] An additional disadvantage of the traditional method of
measuring blood pressure is that it is unable to detect the rate of
change of blood flow as a function of applied pressure. Using the
traditional method, one can readily establish the pressure at which
blood flow through a vessel ceases. However, one cannot determine,
for example, whether the blood velocity began to decrease
precipitously at a particular applied pressure or whether it
decreased gradually throughout the process of applying an external
pressure.
[0012] It is an object of this invention to provide a method and
apparatus for measuring pressure at specific sites in the body in a
non-invasive manner.
[0013] It is a further object of the invention to provide a method
and apparatus for determining the effect of an applied pressure or
blood flow across a broad range of applied pressures.
SUMMARY OF THE INVENTION
[0014] Apparatus and methods are disclosed for non-invasive
measurement of blood velocity in otherwise inaccessible regions,
and for correlating such measurements with externally applied
pressure to detect and/or assess diseases or physiological
abnormalities. The blood velocity measurements can be based on the
Doppler shift that occurs when an ultrasonic wave is scattered by
moving particles within the blood. Since blood vessels have elastic
walls, the geometry of the walls, and therefore the flow dynamics,
will change in response to elevated in vivo pressure. The change in
resistance to blood flow resulting from these pressure induced
changes to the wall geometry can provide a measure of intracranial
pressure, ophthalmic pressure or various other body conditions that
affect blood perfusion. Since wall geometry changes rapidly in
response to such changes in pressure, the invention can be used to
detect hydrocephalus, glaucoma, retinopathy, papilledema and other
physiological abnormalities manifested by pressure changes.
[0015] An apparatus, according to the invention, which uses the
change in blood flow to measure the pressure driving that flow
includes a pressure applicator containing an acoustically
transmitting medium through which ultrasonic waves can propagate
between the blood vessel or other intracorporeal fluid and an
ultrasonic transducer. In one preferred embodiment, the pressure
applicator is a bladder filled with an acoustically transparent
liquid, such as water, and having a deformable side wall which
contacts the skin along a contact area.
[0016] The pressure applicator is preferably coupled to a pressure
sensor, which measures the pressure applied by the pressure
applicator to the surface of the patient, and can be integrated
with, or adapted to couple to, an ultrasonic transducer which
transmits and receives ultrasonic waves.
[0017] Both the pressure applicator and the ultrasonic transducer
are in communication with a data processor which uses the received
pressure data and ultrasonic signal in the conventional manner to
derive the in vivo pressure of the intracorporeal fluid.
[0018] Thus, the invention permits an inferred estimation of in
vivo pressure based on the compliance of the target tissue and
effect of an externally applied pressure on the hemodynamics in the
tissue.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] These and other features, aspects and advantages of the
invention will be better understood with reference to the
accompanying drawings in which:
[0020] FIG. 1 is a schematic perspective view of an ultrasound
probe and pressure measurement apparatus according to the
invention.
[0021] FIG. 2 shows an apparatus according to the invention resting
on the skin covering a fontanelle in a neonatal cranium.
DETAILED DESCRIPTION
[0022] In FIG. 1, a non-invasive pressure measurement apparatus 10
according to the invention includes a hand-held ultrasound probe
12. The geometry of the probe 12 is not critical but can be chosen
for ease of manipulation. Various commercially available ultrasound
systems can be used to provide an ultrasound probe 12 and to
transmit and receive ultrasonic waves, as well as to provide
Doppler shift data. For an exemplary discussion of such ultrasound
systems, see U.S. Pat. No. 5,640,960 which is incorporated herein
by reference.
[0023] A pressure applicator 13, which includes a housing 15 and a
bladder 16 filled with an acoustically transparent medium 18, is
mounted to one end of the ultrasound probe 12 . Preferably, the
bladder is a flexible structure which deforms in response to the
pressure exerted by it bladder on a surface. The acoustically
transparent medium can be water, a saline solution, or any other
acoustically transparent liquid or gel.
[0024] As shown in more detail in FIG. 2, the pressure applicator
13 preferably includes a pressure transducer 19 which is responsive
to the pressure exerted by the bladder on a surface. The pressure
transducer 19 is coupled to a pressure measurement circuit 22, the
output of which becomes an input to a data processor 24. The
pressure applicator 13 can be incorporated into a special purpose
ultrasound probe or designed as an adapter which is coupled to a
conventional probe.
[0025] An ultrasonic transducer 14 incorporated into the probe 12
converts electronic signals into ultrasonic waves that are
transmitted into the medium 18 and, conversely, converts ultrasonic
waves returning back from the medium 18 into electrical signals.
The ultrasonic transducer 14 is electrically coupled to both a
waveform generator 21 and a waveform detector 20. Alternatively,
the functions of the transducer can be performed by one or more
separate transmitters or receivers. A housing 15 can surround the
bladder 16 to constrain deformation of the bladder when pressure is
applied.
[0026] In operation, the clinician positions the pressure
applicator 13 on the skin over the region in which the blood
pressure is to be measured. In FIG. 1, the pressure applicator 13
is shown on the skin 30 covering a fontanelle 36 in a neonatal
cranium 32. The clinician applies an external pressure P.sub.1 by
pressing a contact surface 17 of the pressure applicator 13 against
the skin 30. The pressure thus generated by the operator is
transmitted, by way of the fluid within the bladder 16, to a
pressure transducer 19 which generates an electrical signal
representative of the applied external pressure for processing by
the pressure measurement circuit 22. Accordingly, a pressure
regulation 23 can be used to regulate the pressure applied by the
bladder's contact surface or to implement an automated or
pre-defined protocol of applied pressure. Such a protocol can be
initiated or controlled by data processor 24.
[0027] The above procedure can be performed at sites other than the
illustrated fontanelle. For example, the apparatus 10 can be placed
against a closed eyelid. In such a case, the fluid in the bladder
16 can be acoustically coupled, through the vitreous humor of the
eye, to the capillaries feeding the retina for measurement of blood
pressure in those capillaries.
[0028] The waveform generator 21 transmits an electrical signal to
the transducer 14 which then converts it into an ultrasonic wave.
The ultrasonic wave propagates through the acoustically transparent
medium 18 in the bladder 16 and crosses the skin/bladder interface.
As shown in the illustrative example of FIG. 1, the fontanelle 36,
over which the bladder rests, provides an aperture through which
ultrasonic waves crossing the bladder/skin interface can penetrate
the cranium 32 and illuminate a blood vessel 34. Ultrasonic waves
crossing the bladder/skin interface propagate through the skin 30
and illuminate blood vessels 34 within the brain 38.
[0029] The interaction of the incident ultrasonic radiation with
the blood flow within the blood vessel 34 results in a reflected
ultrasonic wave having a frequency shifted by an amount
representative of the velocity of the blood within the blood
vessel. This Doppler shifted ultrasonic wave exits the cranium
through the fontanelle 36, crosses the interface between the skin
and the bladder, and propagates through the acoustically
transparent medium 18 within the bladder 16. The reflected wave
impinges on the ultrasonic transducer 14 and thereby generates an
electrical signal representative of the reflected wave. This
electrical signal is then transmitted to waveform detector 20.
[0030] The pressure P.sub.1 applied by the operator against the
skin 30 affects the blood velocity in the blood vessel 34. Since
the reflected ultrasonic wave provides a measure of the blood
velocity, this wave is likewise affected by the applied external
pressure P.sub.1. The measured values of the reflected ultrasonic
wave are transmitted to a data processor 24 together with the
measured values of external pressure P.sub.1. The data processor 24
then uses these two quantities to determine the internal pressure
P.sub.2 within the cranium 32.
[0031] It will thus be seen that the invention efficiently attains
the objects set forth above. Since certain changes may be made in
the above construction without departing from the scope of the
invention, it is intended that all matter contained in the above
description or shown in the accompanying drawings be interpreted as
illustrative and not limiting. In particular, the illustration of
measurements at the fontanelle should be understood to be merely
exemplary. The apparatus can be applied to the ophthalmic region to
detect retinopathies or applied to the skin to detect venous
occlusions. Moreover, it may be preferable, in some applications,
to take measurements of the ophthalmic region to detect and/or
assess intracranial abnormalities (particularly, in adults whose
fontanelle regions have fused).
* * * * *